Pathways providing potential sources of saccadic input to the primate superior colliculus were investigated using neuroanatomical tracing techniques. Injections of horseradish peroxidase, a retrograde tracer, were made at various depths within the superior colliculus, including the stratum griseum intermediale, where electrical stimulation elicits saccadic eye movements with low thresholds. Other injections were made above and below this low threshold region. We found that numerous, diverse regions of the brainstem and frontal cortex project to the deep layers of the superior colliculus and subjacent mesencephalic reticular formation. However, sources of subcortical and frontal-cortical input to the intermediate layers of the colliculus are more limited than previously thought. These experiments indicate that three subcortical structures, the substantia nigra, the parabigeminal nucleus, and the rostral mesencephalic reticular formation, and a subregion of prearcuate cortex known as the frontal eye fields may provide the most prominent inputs to the presaccadic cells of the intermediate layers.